Thermostatic automatic choke control for small engines

ABSTRACT

The choke valve of a small engine, biased towards a closed position, is link connected with an air vane that tends to open it under force of cooling air blown across the engine. The air vane has a lost motion connection with a control shaft that is rotatable between defined hot and cold positions. Shaft position is established by two spirally coiled bimetal thermostats, one for high temperatures, one for low temperatures, each in a unidirectional torque transmitting connection between the shaft and fixed structure whereby each thermostat imposes force upon the shaft only at temperatures within its own range.

United States Patent 1191 Thompson et al.

THERMOSTATIC AUTOMATIC CHOKE CONTROL FOR SMALL ENGINES Briggs Stratton Corporation, Wauwatosa, Wis.

Filed: Nov'. 19, 1973 Appl. No.: 417,402-

Assignee:

US. Cl 123/119 F, 261/39 R, 261/39 B Int. Cl. F02b 33/00, F02m 7/00 Field of Search 123/119 F; 261/39 R, 39 B References Cited UNITED STATES PATENTS ,Feb. 4, 1975 3,248,094 4/1966 Ball 123/119 F 3,248,675 4/1966 Furbacher 123/119 F 3,789,814 2/1974 Gillham 123/119 F Primary ExaminerManuel A. Antonakas Assistant ExaminerDaniel J. OConnor [57] ABSTRACT The choke valve of a small engine, biased towards a closed position, is link connected with an air vane that tends to open it under force of cooling air blown across the engine. The air vane has a lost motion connection 'with a control shaft that is rotatable between defined hot and cold positions. Shaft position is established by two spirally coiled bimetal thermostats, one for high temperatures, one for low temperatures, each in a unidirectional torque transmitting connection between the shaft and fixed structure whereby each thermostat imposes force upon the shaft only at temperatures within its own range.

9 Claims, 9 DrawinglFigures PATENTEUFEB 41% 3,863,614

SHEET 10F 6 FELL PATENTED FEB 4197s SHEH 5 OF 6 F'IG.5.

PATENTEDFEKMHTS I 3,863.614

SHEET 80F 6 THERMOSTATIC AUTOMATIC CHOKE CONTROL FOR SMALL ENGINES This invention relates broadly to internal combustion engines, especially engines of the small single-cylinder air-cooled type, and more particularly to an automatic control for the carburetor choke valve of such an en gine. The subject matter of the invention is thus generally like that of the W. E. Armstrong U.S. Pat. No. 2,548,334, issued Apr. l0, 1951.

In the automatic choke control devices of both the Armstrong patent and the present invention, a choke valve is biased towards its closed position and can be sw ung towards its open position by means of an air vane which is responsive to the stream of-engine cooling air that is generated by a blower flywheel on the engine. Swinging of the air vane, and hence of the choke valve, is controlled by a thermostat which has a lost motion connection with the air vane and which is located to be influenced by the heat of the engine.

However, as distinguished from the automatic choke control of the Armstrong patent, the' present invention achieves its objectives with a more simple and more compact structure.

A characterizing feature of the structure of the present invention resides in location of the air vane and the thermostat at opposite end portions of a single rotatably mounted control shaft. The thermostat is seated in a well formed in the cylinder casting, closely adjacent to the engine exhaust port, where the influence of engine heat upon it is assured. The air vane is in the stream of cooling air generated by the conventional blower flywheel on the engine, under the shroud that guides the cooling air across the cylinder body. The control shaft, which comprises a lost motion connection between the thermostat and the air vane, is likewise in an out-of-the way location, most of it being under the blower shroud.

But the main advantage which the automatic choke control of this invention possesses over its predecessor is its ability to provide much more reliable and accurate choke valve positioning throughout a substantially wider range of ambient and engine temperature conditions.

The conventionalthermostat heretofore employed in automatic choke control devices comprised a flat bimetal strip that was coiled into a spiral or a helix. One end of the strip was confined against motion; its other end was attached to a rotatable control member. When the thermostat was subjected to a changing temperature, the control member was rotated in a direction that depended upon whether the temperature change caused the bimetal strip to expand and unwind or to contract and curl up.

When an internal combustion engine is running and fully warmed up, its automatic choke control thermostat is subjected to a temperature in excess of 400F. in a cold engine the thermostat is of course at ambient temperature, which can be anywhere within the range of, say, F. below zero to 80F. or more above zero. This means that for choke control that will afford easy starting under all expectable weather conditions, a thermostat that cooperates with an air vane choke actuator must be capable of fully withstanding the choke opening force exerted by the actuator at the lowest expectable ambient temperature but must permit the choke actuator to take over and swing the choke open little by little as the engine temperature rises through the high ambient range and towards the hot engine temperature. However, when a fully warmed up engine is stopped, the thermostat must hold the choke valve slightly open, against the constantly applied biasing force that tends to swing it closed, for otherwise immediate restarting would be very difficult. Therefore the thermostat means of an automatic choke control device must not only be effective through one temperature range, to control choke opening, but must also be effective in another and substantially higher temperature range to prevent choke closing.

However, the torque force exerted by a coiled bimetal strip varies with temperature at a rate that is (for all practical purposes) uniform throughout its range of response. Since the total rotation to be imparted to a choke valve, for swinging it between its fully open and its fully closed positions, is about the control member that is rotated by a choke control thermostat must be confined to rotation through only a relatively limited angle. The control member must be brought to its high temperature limit of rotation before the engine is fully warmed up, and it must remain in that same rotational position as the engine temperature continues to rise to the fully warmed-up value. Hence, once the control member has reached its high temperature limit of rotation, a single coiled bimetal thermostat like that of the Armstrong patent develops increasing stress with increasing engine temperature.

If it is to provide effective control of choke opening, and especially if it is to afford control that will make for easy starting at very low ambient temperatures, a thermostat bimetal must comprise a. relatively long strip that is coiled into relatively numerous convolutions. In an arrangement like that of the Armstrong patent, the stresses developed in such a strip when the engine comes up to its normal high operating temperature can be great enough to deform it permanently. Once so deformed, the thermostat is of course no longer effective for cold weather starting. With the prior arrangement, the only alternative to risking such deformation of the thermostat was to provide a thermostat that inherently made for poor starting in very cold weather.

This dilemma was in itself sufficient to discourage installation of the choke control of the Armstrong patent on engines that would have to be started in extremely cold weather. But devising an escape from the dilemma was complicated by certain requirements which are imposed by the small engines for which such choke control devices are intended. Every part of a small engine must be extremely compact but sturdy enough to withstand very adverse conditions, and even outright abuse. To add to the difficulties, intense competition in the small engine industry mandates that costs be kept to rock-bottom minimums.

With the foregoing considerations in mind it is a general object of this invention to provide a thermostatic device for automatic choke control that is effective to afford the desired choke valve positioning through the greatest expectable range of ambient temperatures and up to the highest normal engine operating temperatures, without any tendency to be overstressed at either temperature extreme to which it may be subjected; and, moreover, to provide such a thermostatic device that is well suited for small engines by reason of its capability for cooperation with an air vane choke actuator and its compactness, sturdiness and low cost.

From a practical standpoint, therefore, it is an object of this invention to provide a compact, inexpensive, sturdy and reliable automatic choke control for small internal combustion engines that enables an engine on which it is installed to be started easily and promptly in temperatures as low as 20 below zero (Fahrenheit) and also to be readily restarted while hot.

Another object of the invention is to provide such an automatic choke control device which can be readily adjusted by factory and service personnel but which has its relatively delicate thermostat means inaccessible to tampering.

It is also an object of this invention to provide a thermostatic device of general utility, comprising a member which is confined to motion between one limit at which the member is maintained through one range of temperatures and an opposite limit at which it is maintained through another and substantially different range of temperatures, and bimetal strip means so connected with the movable member as to maintain it properly positioned for prevailing temperatures without risk that the bimetal strip means will be subjected to stresses high enough for permanent deformation.

Still another object of this invention is to provide an automatic choke control which can be easily adapted to different carburetor types, as for instance, the updraft carburetors used on engines such as the one illustrated in the Armstrong patent and the horizontal draft type used on engines such as that of the Lechtenberg et al. design patent US. Pat. No. DE. 173,072, wherein the fuel is more easily drawn into the cylinder so that less choking is needed.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a perspective view of a vertical crankshaft engine like that of the aforesaid Letchtenberg et a1 design patent, equipped with the automatic choke control of this invention, a part of the blower housing being shown broken away and the muffler and the air cleaner being omitted from the view;

FIG. 2 is a perspective view of the choke control in its relation to adjacent portions of the engine and carburetor;

FIG. 3 is a side view of the engine cylinder casting per se, with the choke control assembled thereon and the choke valve shown in broken lines;

FIG. 4 is a sectional view taken on the plane of the line 44 in FIG. 3;

FIG. 5 is a fragmentary top view of that portion of the cylinder casting on which the choke control is mounted;

FIG. 6-is a fragmentary bottom view of that portion of the cylinder casting on which the choke control is mounted;

FIG. 7 is an exploded perspective view of the several parts of the control; and

FIGS. 8 and 9 are diagrammatic views illustrating the manner in which the two oppositely acting thermostats function to control choke valve position.

Referring now to the drawings, the numeral 5 designates the cylinder casting of a wellknown single cylinder air cooled engine of the vertical crankshaft type. The crankshaft of the engine has a flywheel 6 mounted on its upper end portion. As is customary, impeller vanes 7 formed on the flywheel induce a flow of cooling air through a blower housing 8 and over the hot surfaces of the engine.

The cylinder casting has the usual intake and exhaust ports 9 and 10, respectively, the latter being threaded to provide for the attachment ofa muffler (not shown) and the former receiving the fuel mixture delivered to the engine by its carburetor, which is generally designated by the numeral 11. The carburetor has an elongated tubular body 12 with flanges 13 at one end thereof which are bolted to the cylinder casting to mount the carburetor. The opposite end of the tubular carburetor body is formed to provide an upwardly facing air inlet port 14 onto which an air cleaner (not shown) is attached. The interior of the tubular carburetor body, between the air inlet port and its discharge end, comprises a mixing passage in which there are the customary venturi and throttle valve, neither of which is shown; and between the throttle valve and the air inlet port is the choke valve 15 of the carburetor, which of course serves to regulate the admission of air into the mixing passage.

Fuel enters the mixing passage from a float bowl 16 at the underside of the tubular body that has a fuel inlet fitting 17 to which a fuel supply line (not shown) connects.

The choke valve 15 is of the butterfly type and hence comprises a disc fixed to a shaft 18 that is journaled in coaxial bores in diametrically opposite side walls of the tubular body, the axis of the shaft being horizontal. For imparting choke valve actuating rotation to the shaft 18, an actuating lever 19 is fixed to its end adjacent to the cylinder casting, and at its other end a weighted lever 20 is fixed to the shaft to bias the choke valve towards a defined closed position.

When the engine is running, the choke valve tends to be opened by an actuator comprising an air vane 21, under the force exerted upon the air vane by the stream of engine cooling air flowing through the blower housing. Thus choke valve opening force is derived in the same way as in the aforesaid Armstrong patent; but instead of the air vane being directly mounted on the choke valve shaft, as it is in the Armstrong patent, the vane 21 is freely rotatably mounted on a vertical control shaft 22 that is in turn rotatably journaled in a bearing boss 23 on the cylinder casting. To enable the vane to swing freely on the control shaft 22, the vane is part of a plastic molding which comprises a choke valve actuator and which has an elongated hub 24 wherein the upper portion of the shaft 22 is received. The vane 21 projects radially from the upper portion of the hub 24. The choke valve actuator also comprises a radially projecting arm on the lower portion of the hub that has its extremity connected by means of a link 26 with the actuating lever 19 on the choke valve shaft. The choke valve and the air vane are thus directly linked, so that the choke valve is constrained to swing in correspondence with rotation of the air vane about the axis of the shaft 22.

It will be apparent that when the engine is not running and the bias provided by the weighted lever arm is not restrained, the choke valve will be in its defined closed position and the air vane will occupy a position extending across the path of the stream of engine cooling air that flows through the blower housing when the engine is in operation.

As best seen in FIGS. 4 and 7, there are abutments 29 and 30 on the control shaft 22, directly above and beneath the boss 23, which cooperate with that boss to confine the shaft against axial displacement without interfering with its free rotation. The lower abutment 30 is provided by a C-washer snapped into a groove in the shaft directly below the underside of the boss, and the upper abutment 29 comprises a pair of diametrically opposite swaged ears projecting from the shaft and seated on a washer 31 that is interposed between those ears and the boss 23.

The control shaft 22 has a transverse slit 32, opening to its bottom end and somewhat elongated axially, to provide for its attachment to a pair of spirally coiled bimetal strips 33 and 34. These bimetal coils comprise the thermostatic control means of this invention that governs the response of the choke valve to the opening force produced by the air vane actuator. To perform their function, the thermostats must be so located as to be sensitive to the heat of the engine in operation. This objective is most effectively achieved with the present invention by locating the thermostats and the lower slitted end portion of the shaft 22 in a cavity 35 formed in a lug 36 that is in close juxtaposition to the exhaust port 10. The lug 36 can comprise a separate part suitably secured to the cylinder casting, but it is preferably formed integrally with that casting, as shown.

The cavity 35 is a two-diameter cylindrical well which opens to the underside of the lug 36 and which is coaxial with the bore through the lug 23 that constrains the shaft 22 to rotation. In the end wall of the cylindrical well there is a hole which is concentric with the cavity and through which the control shaft 22 projects into the cavity with a close but freely rotatable fit. The axially innermost small diameter upper portion 37 of the cylindrical well is axially shorter than the large diameter lower portion 38 thereof. The bimetal coil 33, which is the smaller of the two and can be considered a hot thermostat, is received in the upper portion 37 of the cylindrical cavity; the cold thermostat 34 is received in the larger lower portion of the cavity.

The mouth of the-cylindrical well or cavity 35 is closed by a Welsh plug 41, to preclude tampering with the bimetal elements.

The inner convolutions ofthe bimetal coils have radially in-turned end portions that are seated in the slit 32 in the control shaft 22, so that as the coils wind and unwind they can impart torque to the control shaft.

As best seen in FIGS. 6, 8 and 9, each of the well portions is formed with a shoulder 39, 39' that projects radially inwardly from its cylindrical side wall. These shoulders provide stops against which radially outturned end portions of the outer convolutions of the two spirally coiled bimetal strips 33, 34 can abut and react as the coils wind and unwind in response to temperature changes. It is to be observed, however, that the shoulders 39, 39 provide unidirectional connections between the bimetal strips and the fixed structure comprising the lug 36, so that each of the thermostats can impose torque upon the control shaft 22 in only one direction of its rotation. The shoulders 39, 39' face in opposite directions, and the two bimetal elements are oppositely coiled and also have their higher coefficients of expansion at opposite faces. Hence, as explained hereinafter, the bimetal coils alternate with one another in controlling the rotational orientation of the control shaft 22.

To guard against interference between the coils of the superimposed bimetal elements, a washer 40 is interposed between them.

As noted hereinbefore, the choke valve is constrained to move with the choke valve actuator that comprises the air vane 21 and its hub 24, but the choke valve actuator is free to turn with respect to the shaft 22 to which the thermostats are connected. To enable the thermostats to limit opening of the choke valve in response to the opening force exerted upon the air vane by the stream of cooling air that impinges it, there is a lost motion connection between the control shaft 22 and the choke valve actuator. One element of the lost motion connection comprises a finger 28 which is formed integrally with the plastic molding and which projects radially inwardly from the air vane across the top of its hub 24. The other element of the lost motion connection comprises an angularly slotted collar 43 which is angularly adjustably fixed to the upper end portion of the control shaft 22 and which overlies the upper end of the hub portion 24.. An angular slot 44 in the peripheral portion of the collar 43 accommodates the fin or finger 28.

As will be readily understood, the circumferential length of the slot 44 determines the extent of rotary lost motion between the air vane and the control shaft 22, and the angular position of the collar 43 on the shaft 22 determines the relationship of the lost motion with respect to the effect of the thermostatic elements upon the shaft position.

The angle through which the control shaft 22 can turn in response to the balance of the several torque producing forces exerted upon it by the air vane actuator, the weighted arm 20 and the thermostatic elements is limited by a second circumferentially slotted collar 47, adjustably fixed to the shaft 22 beneath the hub portion 24 of the air vane unit and just above the swaged ears 29. To define the limits of rotation of the control shaft 22, the ends of an arcuate slot 46 in the collar 47 collide with a stop fin 48 that projects from the top of the boss 23.

It will be apparent that rotational adjustment of the collar 47 on the control shaft 22 establishes the temperature range at which that shaft tends to be maintained at each of its limits of rotation. The adjustability of that collar thus enables the automatic choke control device of this invention to be readily adapted for installation on different types of carburetors, as for example updraft carburetors which require relatively heavy choking and horizontal draft carburetors which require less choking. Rotational adjustment of the collar 43 on the control shaft enables the automatic choke device to be readily mated with any particular linkage between a choke actuator and a choke valve.

Since the hub portion 24 of the plastic molding is axially confined between the collars 43 and 47, both of which are fixed to the shaft 22, those collars confine the plastic molding to rotation relative to the control shaft.

, expands and unwinds. The shoulders 39, 39' face in opposite circumferential directions such that each shoulder takes the reaction to unwinding or expansion of the bimetal coil with which it cooperates.

As seen in FIGS. 8 and 9, the control shaft 22 rotates clockwise towards its high temperature range rotational position, at which it permits full opening of the choke valve.

When the engine is cold, the larger cold coil 33 reacts between its shoulder 39 and the control shaft to urge the control shaft towards its low temperature range position at which the air vane choke actuator is inhibited from opening the choke valve. At very cold ambient temperatures the cold coil 33 exerts sufficient torque force upon the control shaft 22 to substantially prevent movement of the choke actuator. and thus hold the choke closed or nearly closed even when the engine is running. As temperature increase from the very cold ambient level, the cold coil gradually contracts and winds up, decreasing its torque force upon the control shaft and thus allowing the air vane actuator to take over and swing the choke valve towards its open position in step with the rising temperatures. As the temperature rises above the highest level at which the choke valve should be restrained against fully opening, the cold coil curls or winds up enough to disengage itself from its shoulder 39, so that the cold coil is not subjected to any externally imposed stress at such high tempeatures.

Meanwhile, the hot coil 33 is functioning in a manner opposite to the operation of the cold coil, inasmuch as it unwinds or tends to straighten out upon heating and exerts torque force upon the control shaft 22 only at high temperatures. Thus, when the engine is hot, the hot coil holds the control shaft 22 at its high temperature position of rotation. The choke valve is then held slightly open when the engine is stopped and can be fully opened by the air vane actuator as soon as the engine begins to run. At lower temperatures the cold coil controls the rotational position of the shaft 22, and the hot coil is disengaged from its shoulder 39 so as not to be subjected to any externally imposed stress.

It will be apparent that each bimetal coil is subjected to only a limited externally imposed stress, not high enough to permanently deform it, owing to the fact that each coil exerts torque upon the control shaft 22 through only a relatively narrow range of temperatures.

Merely for the sake of illustration, the small hot thermostat 33 can consist of about four turns of onequarter inch wide bimetal strip, and the larger cold thermostat 34 can comprise seven turns of threeeighths inch wide bimetal strip.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides an automatic choke device for small engines that is simple, compact, tamper proof, and capable of reliably affording choke control under a wide range of ambient temperatures.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims.

We claim:

1. in an internal combustion engine having relatively fixed structure comprising a carburetor with an air inlet duct and having a choke valve in said air inlet duct which is movable between defined open and closed positions and isbiased towards its closed position, an automatic control for the choke valve comprising:

A. actuating means operable to produce a choke valve opening force in response to engine speed;

B. motion transmitting means connecting said actuating means with the choke valve and through which said force can be imposed upon the choke valve to urge it towards its open position against its bias;

C. a control member constrained to move in opposite directions between defined limits;

D. means providing a lost motion connection between said control member and the choke valve whereby the choke valve is prevented from moving to its open position when the control member is confined at one of said limits and is prevented from moving to its closed position when the control member is confined at the other of said limits;

E. first thermostatic means positioned to be influenced by the heat developed by the engine and by which a first choke valve controlling force can be exerted which diminishes at one rate with increasing engine temperature;

F. means connecting said first thermostatic means between the fixed structure and the control member to react between them in response to decreasing temperatures and in the direction to urge the control member towards its said one limit, said connecting means comprising a unidirectional force transmitting connection which prevents the first thermostatic means from imposing force upon the control member in the direction to urge it towards its other limit;

G. second thermostatic means positioned to be influenced by the heat developed by the engine and by which a second choke valve controlling force can be exerted which increases, but at a lower rate, with increasing temperature; and

H. means connecting said second thermostatic means between the fixed structure and the control member to react between them in response to increasing temperatures and in the direction to urge the control member towards its said other limit, the last mentioned connecting means comprising a unidirectional force transmitting connection which prevents the second thermostatic means from imposing force upon the control member in the direction to urge it towards its said one limit.

2. The automatic choke valve control of claim 1,

wherein:

1. said control member comprises a shaft constrained to rotation, and

2. each of said thermostatic means comprises a spirally coiled bimetal strip encircling said shaft and having its innermost convolution attached to the shaft and its outermost convolution restrained against rotation about the shaft in one direction.

3. The automatic choke valve control of claim 2, in combination with an internal combustion engine having a cylinder member which heats during operation of the engine, further characterized by:

3. means on the cylinder member, in heat conducting relation thereto, defining a cavity in which said two spirally coiled bimetal strips are seated in axially superimposed relationship and into which an end portion of said shaft projects for connection to the bimetal strips.

4. The automatic choke valve control of claim 3, further characterized by:

4. said shaft having in its said end portion an axially extending transverse slot in which is received an end portion of each of said bimetal strips, adjacent to the innermost convolution thereof, to attach the strip to the shaft, and

5. a washer in said cavity, between the spirally coiled strips and surrounding the shaft.

5. The automatic choke valve control of claim 4, further characterized by said unidirectional force transmitting connections comprising:

a. means on side wall portions of said cavity defining an abutment for each thermostatic means, each abutment facing substantially circumferentially inone direction; and

b. a radially outturned end portion on the outermost convolution of each coiled bimetal strip, flatwise engageable with its abutment.

6. The automatic choke valve control of claim 2, in combination with an engine having a blower that generates a stream of cooling air when the engine is in operation, further characterized by:

3. said actuating means comprising an air vane upon which flatwise swinging force in one direction can be exerted by the stream ofcooling air,

4. means journaling said air vane on said shaft for flatwise swinging motion of the air vane relative to the shaft and disposing the. air vane in the stream of cooling air from the blower, and

5. said lost motion connection means comprising cooperating abutment members which are respectively constrained to move with the shaft and with the air vane and which define limits of swinging motion of the air vane relative to the shaft.

7. The automatic choke valve control of claim 6 wherein the choke valve is fixed on a butterfly shaft having an end portion that projects outside the air inlet duct, further characterized by:

6. said means journaling the air vane for swinging motion comprising a substantially tubular hub portion on the air vane which embraces a portion of the shaft, and

7. said motion transmitting means comprising a. a projecting arm fixed on said tubular hub portion to move in unison therewith;

b. another radially projecting arm fixed on the butterfly shaft, and

c. a link connecting said arms.

8. In an internal combustion engine having relatively fixed structure comprising a carburetor with an air inlet duct and having a choke valve in said air inlet duct which is movable between defined open and closed poan automatic control for the choke valve comprising:

A. actuating means operable to produce in response to engine speed a choke valve opening force that can overcome the bias on the choke valve;

B. motion transmitting means connecting said actuating means with the choke valve and through which said force can be imposed upon the choke valve to urge it towards its open position;

C. a control member constrained to move in opposite directions between defined limits;

D. means providing a lost motion connection between said control member and the choke valve whereby the choke valve is prevented from moving to its open position when the control member is confined at one of said limits and is prevented from moving to its closed position when the control member is confined at the other of said limits;

E. a pair of thermostatic elements positioned to be influenced by'heat developed by the engine and each capable of exerting a force in response toa change in the temperature to which it is subjected, one of said thermostatic elements being for high temperaturs, the other for low ones; and

F. means connecting each of said thermostatic ele ments between the fixed structure and the control member to produce a force exerting reaction between them in only one direction, the last mentioned means comprising a unidirectional force transmitting connection for each thermostatic element,

1. the unidirectional forcetransmitting connection for the low temperature thermostatic element being so arranged that the force which the low temperature thermostatic element exerts in response to decreasing temperatures is imposed upon the control member in the direction to urge the same towards said one limit, and

2. the unidrectional force transmitting connection for the high temperature thermostatic element being so arranged that the force which the high temperature thermostatic element exerts in re sponse to increasing temperatures is imposed upon the control member in the direction to urge the same towards its said other limit.

9. The automatic choke control of claim 8, further characterized by:

1. said control member being constrained to rotation between said limits;

2. each of said thermostatic elements comprising a coiled bimetal strip that can exert torque forces by winding up and unwinding in response to changing temperature/and 3. the bimetal strip comprising said low tempera ture thermostatic element having a greater projected length than that comprising the high temperature thermostatic element, so that with a given change in temperature the torque force exerted by the low temperature thermostatic element changes more than that exerted by the high temperature thermostatic element. 

1. said control member comprises a shaft constrained to rotation, and
 1. the unidirectional force transmitting connection for the low temperature thermostatic element being so arranged that the force which the low temperature thermostatic element exerts in response to decreasing temperatures is imposed upon the control member in the direction to urge the same towards said one limit, and
 1. said control member being constrained to rotation between said limits;
 1. In an internal combustion engine having relatively fixed structure comprising a carburetor with an air inlet duct and having a choke valve in said air inlet duct which is movable between defined open and closed positions and is biased towards its closed position, an automatic control for the choke valve comprising: A. actuating means operable to produce a choke valve opening force in response to engine speed; B. motion transmitting means connecting said actuating means with the choke valve and through which said force can be imposed upon the choke valve to urge it towards its open position against its bias; C. a control member constrained to move in opposite directions between defined limits; D. means providing a lost motion connection between said control member and the choke valve whereby the choke valve is prevented from moving to its open position when the control member is confined at one of said limits and is prevented from moving to its closed position when the control member is confined at the other of said limits; E. first thermostatic means positioned to be influenced by the heat developed by the engine and by which a first choke valve controlling force can be exerted which diminishes at one rate with increasing engine temperature; F. means connecting said first thermostatic means between the fixed structure and the control member to react between them in response to decreasing temperatures and in the direction to urge the control member towards its said one limit, said connecting means comprising a unidirectional force transmitting connection which prevents the first thermostatic means from imposing force upon the control member in the direction to urge it towards its other limit; G. second thermostatic means positioned to be influenced by the heat developed by the engine and by which a second choke valve controlling force can be exerted which increases, but at a lower rate, with increasing temperature; and H. means connecting said second thermostatic means between the fixed structure and the control member to react between them in response to increasing temperatures and in the direction to urge the control member towards its said other limit, the last mentioned connecting means comprising a unidirectional force transmitting connection which prevents the second thermostatic means from imposing force upon the control member in the direction to urge It towards its said one limit.
 2. each of said thermostatic elements comprising a coiled bimetal strip that can exert torque forces by winding up and unwinding in response to changing temperature; and
 2. The automatic choke valve control of claim 1, wherein:
 2. the unidrectional force transmitting connection for the high temperature thermostatic element being so arranged that the force which the high temperature thermostatic element exerts in response to increasing temperatures is imposed upon the control member in the direction to urge the same towards its said other limit.
 2. each of said thermostatic means comprises a spirally coiled bimetal strip encircling said shaft and having its innermost convolution attached to the shaft and its outermost convolution restrained against rotation about the shaft in one direction.
 3. The automatic choke valve control of claim 2, in combination with an internal combustion engine having a cylinder member which heats during operation of the engine, further characterized by:
 3. means on the cylinder member, in heat conducting relation thereto, defining a cavity in which said two spirally coiled bimetal strips are seated in axially superimposed relationship and into which an end portion of said shaft projects for connection to the bimetal strips.
 3. said actuating means comprising an air vane upon which flatwise swinging force in one direction can be exerted by the stream of cooling air,
 3. the bimetal strip comprising said low temperature thermostatic element having a greater projected length than that comprising the high temperature thermostatic element, so that with a given change in temperature the torque force exerted by the low temperature thermostatic element changes more than that exerted by the high temperature thermostatic element.
 4. means journaling said air vane on said shaft for flatwise swinging motion of the air vane relative to the shaft and disposing the air vane in the stream of cooling air from the blower, and
 4. The automatic choke valve control of claim 3, further characterized by:
 4. said shaft having in its said end portion an axially extending transverse slot in which is received an end portion of each of said bimetal strips, adjacent to the innermost convolution thereof, to attach the strip to the shaft, and
 5. a washer in said cavity, between the spirally coiled strips and surrounding the shaft.
 5. said lost motion connection means comprising cooperating abutment members which are respectively constrained to move with the shaft and with the air vane and which define limits of swinging motion of the air vane relative to the shaft.
 5. The automatic choke valve control of claim 4, further characterized by said unidirectional force transmitting connections comprising: a. means on side wall portions of said cavity defining an abutment for each thermostatic means, each abutment facing substantially circumferentially in one direction; and b. a radially outturned end portion on the outermost convolution of each coiled bimetal strip, flatwise engageable with its abutment.
 6. The automatic choke valve control of claim 2, in combination with an engine having a blower that generates a stream of cooling air when the engine is in operation, further characterized by:
 6. said means journaling the air vane for swinging motion comprising a substantially tubular hub portion on the air vane which embraces a portion of the shaft, and
 7. said motion transmitting means comprising a. a projecting arm fixed on said tubular hub portion to move in unison therewith; b. another radially projecting arm fixed on the butterfly shaft, and c. a link connecting said arms.
 7. The automatic choke valve control of claim 6 wherein the choke valve is fixed on a butterfly shaft having an end portion that projects outside the air inlet duct, further characterized by:
 8. In an internal combustion engine having relatively fixed structure comprising a carburetor with an air inlet duct and having a choke valve in said air inlet duct which is movable between defined open and closed positions and which is biased towards its closed position, an automatic control for the choke valve comprising: A. actuating means operable to produce in response to engine speed a choke valve opening force that can overcome the bias on the choke valve; B. motion transmitting means connecting said actuating means with the choke valve and through which said force can be imposed upon the choke valve to urge it towards its open position; C. a control member constrained to move in opposite directions between defined limits; D. means providing a lost motion connection between said control member and the choke valve whereby the choke valve is prevented from moving to its open position when the control member is confined at one of said limits and is prevented from moving to its closed position when the control member is confined at the other of said limits; E. a pair of thermostatic elements positioned to be influenced by heat developed by the engine and each capable of exerting a force in response to a change in the temperature to which it is subjected, one of said thermostatic elements being for high temperaturs, the other for low ones; and F. means connecting each of said thermostatic elements between the fixed structure and the control member to produce a force exerting reaction between them in only one direction, the last mentioned means comprising a unidirectional force transmitting connection for each thermostatic element,
 1. the unidirectional force transmitting connection for the low temperature thermostatic element being so arranged that the force which the low temperature thermostatic element exerts in response to decreasing temperatures is imposed upon the control member in the direction to urge the same towards said one limit, and
 2. the unidrectional force transmitting connection for the high temperature thermostatic element being so arranged that the force which the high temperature thermostatic element exerts in response to increasing temperatures is imposed upon the control member in the direction to urge the same towards its said other limit.
 9. The automatic choke control of claim 8, further characterized by: 